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Research and Development of Additive Manufacturing Technology
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Research and Development of Additive Manufacturing Technology

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Manufacturing Processes and Systems".

Deadline for manuscript submissions: closed (20 November 2022) | Viewed by 34346

Special Issue Editors

Prof. Dr. Volker Schulze

E-Mail Website
Guest Editor
Karlsruhe Institute of Technology, Institute for Applied Materials (IAM), Karlsruhe, Germany
Interests: production technology; manufacturing engineering; materials technology
Dr. Frederik Zanger

E-Mail Website
Guest Editor
Karlsruhe Institute of Technology, Karlsruhe, Germany
Interests: surface engineering; machining; manufacturing technology

Special Issue Information

Dear Colleagues,

In this Special Issue, we are looking for recent findings in the field of additive manufacturing focusing on process technologies and process chains. Parts of or complete process chains are to be considered, starting with material production and additive manufacturing processes up to the manufacturing of functional surfaces with narrow tolerances or special requirements on surface integrity. Articles presenting results with significant progress in one of the areas of material development, (hybrid) process technology, process strategy, (hybrid) machine tool, process monitoring and control or metrology for additively manufactured components will be considered.

Prof. Dr. Volker Schulze
Dr. Frederik Zanger
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • additive manufacturing
  • powder bed processes
  • directed energy deposition processes
  • binder jetting processes
  • process chains

Published Papers (14 papers)

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Research

15 pages, 13425 KiB  
Article
Molecular Dynamics Simulation of NiTi Shape Memory Alloys Produced by Laser Powder Bed Fusion: Laser Parameters on Phase Transformation Behavior
by Guotai Li, Tianyu Yu, Pan Wu and Mingjun Chen
Materials 2023, 16(1), 409; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16010409 - 01 Jan 2023
Cited by 4 | Viewed by 2005
Abstract
In this study, the deposition, powder spreading, and laser fusion processes during the laser powder bed fusion (L-PBF) process were studied using molecular dynamics (MD) simulation. The effect of Ni content on the characteristic phase transformation temperatures was also investigated. Shape memory effect [...] Read more.
In this study, the deposition, powder spreading, and laser fusion processes during the laser powder bed fusion (L-PBF) process were studied using molecular dynamics (MD) simulation. The effect of Ni content on the characteristic phase transformation temperatures was also investigated. Shape memory effect and superelasticity of NiTi alloys with Ni content ranged from 48.0% to 51.0% were analyzed. By employing MEAM potentials, the effects of the laser power, spot diameter, and scanning speed on the molten pool size and element evaporation were studied. Simulation results showed that a larger spot diameter renders a higher Ni content in the molten pool, also a larger molten pool. A faster scanning speed leads to a higher Ni content in the molten pool, and a smaller molten pool. The element is difficult to evaporate using small laser power and a large spot diameter. The element in the molten pool expresses a great evaporation effect when the Es is larger than 0.4 eV/ų. According to Ni content within the molten pool during laser fusion, characteristic phase transition temperatures in single crystalline NiTi alloys with variant Ni content were investigated by employing a 2NN-MEAM potential. Characteristic phase transition temperature changes as the Ni content increases from 48.0% to 51.0%. Austenite boundaries and Ni content in the boundary were found to be the keys for controlling the characteristic phase transformation temperature. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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18 pages, 11653 KiB  
Article
PBF-LB/M of Low-Alloyed Steels: Bainite-like Microstructures despite High Cooling Rates
by Dominic Bartels, Tobias Novotny, Andreas Mohr, Frank van Soest, Oliver Hentschel, Carsten Merklein and Michael Schmidt
Materials 2022, 15(17), 6171; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15176171 - 05 Sep 2022
Cited by 5 | Viewed by 1634
Abstract
Laser-based powder bed fusion of metals (PBF-LB/M) is an emerging technology with enormous potential for the fabrication of highly complex products due to the layer-wise fabrication process. Low-alloyed steels have recently gained interest due to their wide potential range of applications. However, the [...] Read more.
Laser-based powder bed fusion of metals (PBF-LB/M) is an emerging technology with enormous potential for the fabrication of highly complex products due to the layer-wise fabrication process. Low-alloyed steels have recently gained interest due to their wide potential range of applications. However, the correlation between the processing strategy and the material properties remains mostly unclear. The process-inherent high cooling rates support the assumption that a very fine martensitic microstructure is formed. Therefore, the microstructure formation was studied by means of scanning electron microscopy, hardness measurements, and an analysis of the tempering stability. It could be shown that additively manufactured Bainidur AM samples possess a bainitic microstructure despite the high process-specific cooling rates in PBF-LB/M. This bainitic microstructure is characterized by an excellent tempering stability up to temperatures as high as 600 °C. In contrast to this, additively manufactured and martensitic-hardened specimens are characterized by a higher initial hardness but a significantly reduced tempering stability. This shows the potential of manufacturing products from Bainidur AM for high-temperature applications without the necessity of a post-process heat treatment for achieving the desired bainitic microstructure. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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12 pages, 6093 KiB  
Article
Effect of Rapid Heating and Cooling Conditions on Microstructure Formation in Powder Bed Fusion of Al-Si Hypoeutectic Alloy: A Phase-Field Study
by Masayuki Okugawa, Yuya Furushiro and Yuichiro Koizumi
Materials 2022, 15(17), 6092; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15176092 - 02 Sep 2022
Cited by 8 | Viewed by 1779
Abstract
Al alloy parts fabricated by powder bed fusion (PBF) have attracted much attention because of the degrees of freedom in both shapes and mechanical properties. We previously reported that the Si regions in Al-Si alloy that remain after the rapid remelting process in [...] Read more.
Al alloy parts fabricated by powder bed fusion (PBF) have attracted much attention because of the degrees of freedom in both shapes and mechanical properties. We previously reported that the Si regions in Al-Si alloy that remain after the rapid remelting process in PBF act as intrinsic heterogeneous nucleation sites during the subsequent resolidification. This suggests that the Si particles are crucial for a novel grain refinement strategy. To provide guidelines for grain refinement, the effects of solidification, remelting, and resolidification conditions on microstructures were investigated by multiphase-field simulation. We revealed that the resolidification microstructure is determined by the size and number of Si regions in the initial solidification microstructures and by the threshold size for the nucleation site, depending on the remelting and resolidification conditions. Furthermore, the most refined microstructure with the average grain size of 4.8 µm is predicted to be formed under conditions with a large temperature gradient of Gsol = 106 K/m in the initial solidification, a high heating rate of HR = 105 K/s in the remelting process, and a fast solidification rate of Rresol = 10−1 m/s in the resolidification process. Each of these conditions is necessary to be considered to control the microstructures of Al-Si alloys fabricated via PBF. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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17 pages, 8813 KiB  
Article
Removal of Stair-Step Effects in Binder Jetting Additive Manufacturing Using Grayscale and Dithering-Based Droplet Distribution
by Christoph Hartmann, Lucas van den Bosch, Johannes Spiegel, Dominik Rumschöttel and Daniel Günther
Materials 2022, 15(11), 3798; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15113798 - 26 May 2022
Cited by 4 | Viewed by 3930
Abstract
Binder jetting is a layer-based additive manufacturing process for three-dimensional parts in which a print head selectively deposits binder onto a thin layer of powder. After the deposition of the binder, a new layer of powder is applied. This process repeats to create [...] Read more.
Binder jetting is a layer-based additive manufacturing process for three-dimensional parts in which a print head selectively deposits binder onto a thin layer of powder. After the deposition of the binder, a new layer of powder is applied. This process repeats to create three-dimensional parts. The binder jetting principle can be adapted to many different materials. Its advantages are the high productivity and the high degree of freedom of design without the need for support structures. In this work, the combination of binder jetting and casting is utilized to fabricate metal parts. However, the achieved properties of binder jetting parts limit the potential of this technology, specifically regarding surface quality. The most apparent surface phenomenon is the so-called stair-step effect. It is considered an inherent feature of the process and only treatable by post-processing. This paper presents a method to remove the stair-step effect entirely in a binder jetting process. The result is achieved by controlling the binder saturation of the individual voxel volumes by either over or underfilling them. The saturation is controlled by droplet size variation as well as dithering, creating a controlled migration of the binder between powder particles. This work applies the approach to silica sand particle material with an organic binder for casting molds and cores. The results prove the effectiveness of this approach and outline a field of research not identified previously. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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13 pages, 4045 KiB  
Article
Inverse Determination of Johnson–Cook Parameters of Additively Produced Anisotropic Maraging Steel
by Rocco Eisseler, Daniel Gutsche, Clemens Maucher and Hans-Christian Möhring
Materials 2022, 15(1), 26; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15010026 - 21 Dec 2021
Cited by 2 | Viewed by 2275
Abstract
In powder bed-based additive manufacturing (AM), complex geometries can be produced in a layer-wise approach. Results of material science experiments regarding material property identification, e.g., tensile strength, show interdependencies between the test load direction and the layer orientation. This goes hand-in-hand with the [...] Read more.
In powder bed-based additive manufacturing (AM), complex geometries can be produced in a layer-wise approach. Results of material science experiments regarding material property identification, e.g., tensile strength, show interdependencies between the test load direction and the layer orientation. This goes hand-in-hand with the measured cutting force, changing with the relative angle between cutting direction and layer orientation in orthogonal cutting tests. However, due to the specific process characteristics, the layer orientation results in anisotropic material properties. Therefore, during machining, the material behaves depending on the buildup direction, which influences the cutting process. To predict this behavior, a simplified inverse approach is developed to determine the buildup direction-dependent parameters of a modified Johnson–Cook model for cutting simulation. To qualify these cutting models, mainly the cutting force and additionally the chip formation examined during orthogonal cuts are used. In the present paper, the influence of the laser-powder-bed-fusion (LPBF) process parameters on subtractive post-processing are shown. A good agreement between verification experiments and simulations is achieved. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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10 pages, 3005 KiB  
Article
PBF-LB Process-Induced Regular Cavities for Lightweight AlSi10Mg Structures
by Victor Lubkowitz, Jonas Alber and Frederik Zanger
Materials 2021, 14(21), 6665; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14216665 - 05 Nov 2021
Cited by 1 | Viewed by 1804
Abstract
In powder bed fusion with laser beam (PBF-LB), two process-induced defects by pore formation are known: local spherical pores by the keyhole effect and geometrically undefined pores caused by lack of fusion. Both pore types are heterogeneously distributed and can be used for [...] Read more.
In powder bed fusion with laser beam (PBF-LB), two process-induced defects by pore formation are known: local spherical pores by the keyhole effect and geometrically undefined pores caused by lack of fusion. Both pore types are heterogeneously distributed and can be used for lightweight or damping design applications. The achievable porosity is limited to around 13%. This article presents a novel process-controlled method enabling the targeted and reproducible manufacturing of solid parts with regularly distributed cavities, currently up to 60% porosity in AlSi10Mg, using the balling effect. This eliminates the need for time-consuming digital pre-processing work. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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17 pages, 20327 KiB  
Article
Process Window for Highly Efficient Laser-Based Powder Bed Fusion of AlSi10Mg with Reduced Pore Formation
by Artur Leis, Rudolf Weber and Thomas Graf
Materials 2021, 14(18), 5255; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14185255 - 13 Sep 2021
Cited by 10 | Viewed by 1921
Abstract
The process window for highly efficient laser-based powder bed fusion (LPBF), ensuring the production of parts with low porosity, was determined by analyzing cross-sections of samples that were generated with laser powers varying between 10.8 W and 1754 W, laser beam diameters varying [...] Read more.
The process window for highly efficient laser-based powder bed fusion (LPBF), ensuring the production of parts with low porosity, was determined by analyzing cross-sections of samples that were generated with laser powers varying between 10.8 W and 1754 W, laser beam diameters varying between 35 μm and 200 μm, and velocities of the moving laser beam ranging between 0.7 m/s and 1.3 m/s. With these parameters, the process alters between different modes that are referred to as simple heating, heat conduction melting (HCM), key-bowl melting (KBM), and deep-penetration melting (DPM). It was found that the optimum process window for a highly efficient LPBF process, generating AlSi10Mg parts with low porosity, is determined by the ratio PL/db of the incident laser power PL and the beam diameter db of the beam on the surface of the bead, and ranges between PL/db = 2000 W/mm and PL/db = 5200 W/mm, showing process efficiencies of about 7–8%. This optimum process window is centered around the range PL/db = 3000–3500 W/mm, in which the process is characterized by KBM, which is an intermediate process mode between HCM and DPM. Processes with PL/db < 2000 W/mm partially failed, and lead to balling and a lack of fusion, whereas processes with PL/db > 5200 W/mm showed a process efficiency below 5% and pore ratios exceeding 10%. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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18 pages, 26706 KiB  
Article
Formation of Structure and Properties of Two-Phase Ti-6Al-4V Alloy during Cold Metal Transfer Additive Deposition with Interpass Forging
by Yuri Shchitsyn, Maksim Kartashev, Ekaterina Krivonosova, Tatyana Olshanskaya and Dmitriy Trushnikov
Materials 2021, 14(16), 4415; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14164415 - 06 Aug 2021
Cited by 16 | Viewed by 1756
Abstract
The paper deals with the main formation patterns of structure and properties of a titanium alloy of the Ti-6Al-4V system during additive manufacturing using cold metal transfer (CMT) wire deposition. The work aims to find the optimal conditions for layer-by-layer deposition, which provides [...] Read more.
The paper deals with the main formation patterns of structure and properties of a titanium alloy of the Ti-6Al-4V system during additive manufacturing using cold metal transfer (CMT) wire deposition. The work aims to find the optimal conditions for layer-by-layer deposition, which provides the high physical and mechanical properties of the titanium alloy of the Ti-6Al-4V system hybrid, additively manufactured using CMT deposition. Particular attention is paid to interpass forging during the layered printing of the product. Additionally, we investigate how the heat treatment affects the structure and properties of the Ti-6Al-4V alloy that has been CMT-deposited, both with and without forging. These studies have shown that the hybrid multilayer arc deposition technology, with interpass strain hardening, allows the use of high temperature and high technology titanium alloys to obtain products of a required geometric shape. It has been proven that the interpass deformation effect during CMT deposition contributes to a significant decrease in the sizes of the primary β-grains. In addition, forging enhances the effect of microstructure refinement, which is associated with phase recrystallization in deformed areas. It is shown that the heat treatment leads not only to a change in the morphology of the phases but also to additional phase formations in the structure of the Ti-6Al-4V-deposited metal while the mechanism is realized and consists of the gradual decomposition of the martensitic α′-phase and the formation of a dispersive α2-phase. This structure formation process is accompanied by the dispersion hardening of the α-phase. The strength characteristics of the Ti-6Al-4V alloy obtained using layer-by-layer CMT with forging are given; they exceed the strength level of materials obtained with the traditional technologies of pressure treatment, and there is no decrease in plasticity characteristics. The use of the subsequent heat treatment makes it possible to increase the ductility characteristics of the deposited and forged Ti-6Al-4V material by 1.5–2 times without strength loss. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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18 pages, 10335 KiB  
Article
Fused Filament Fabrication of NiTi Components and Hybridization with Laser Powder Bed Fusion for Filigree Structures
by Johannes Abel, Anne Mannschatz, Robert Teuber, Bernhard Müller, Omar Al Noaimy, Sebastian Riecker, Juliane Thielsch, Björn Matthey and Thomas Weißgärber
Materials 2021, 14(16), 4399; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14164399 - 06 Aug 2021
Cited by 2 | Viewed by 2560
Abstract
The present study introduces an approach to the powder metallurgical shaping of a pseudo-elastic nickel–titanium (NiTi 44 alloy) combining two different Additive Manufacturing (AM) processes, namely fused filament fabrication (FFF) and Laser Powder Bed Fusion (LPBF), by manufacturing filigree structures on top of [...] Read more.
The present study introduces an approach to the powder metallurgical shaping of a pseudo-elastic nickel–titanium (NiTi 44 alloy) combining two different Additive Manufacturing (AM) processes, namely fused filament fabrication (FFF) and Laser Powder Bed Fusion (LPBF), by manufacturing filigree structures on top of sintered FFF parts. Both processes start with commercial gas atomized NiTi powder, which is fractionated into two classes. Using the fine fraction with particle sizes <15 µm, robust thermoplastic filaments based on a non-commercial binder system were produced and processed to different auxetic and non-auxetic geometries employing a commercial standard printer. FTIR analysis for thermal decomposition products was used to develop a debinding regime. After sintering, the phase transformation austenite/martensite was characterized by DSC in as sintered and annealed state. Precipitates resulting from residual impurities were detected by micrographs and XRD. They led to an increased transformation temperature. Adjusting the oxygen and carbon content in the alloy remains a challenging issue for powder metallurgical processed NiTi alloys. Filigree lattice structures were built onto the surfaces of the sintered FFF parts by LPBF using the coarser powder fraction (15–45 µm). A good material bond was formed, resulting in the first known NiTi hybrid, which introduces new production and design options for future applications. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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18 pages, 10440 KiB  
Article
Dual-Laser PBF-LB Processing of a High-Performance Maraging Tool Steel FeNiCoMoVTiAl
by Gregor Graf, Niki Nouri, Stefan Dietrich, Frederik Zanger and Volker Schulze
Materials 2021, 14(15), 4251; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14154251 - 29 Jul 2021
Cited by 11 | Viewed by 3479
Abstract
As part of an international research project (HiPTSLAM), the development and holistic processing of high-performance tool steels for AM is a promising topic regarding the acceptance of the laser powder bed fusion (PBF-LB) technology for functionally optimized die, forming and cutting tools. In [...] Read more.
As part of an international research project (HiPTSLAM), the development and holistic processing of high-performance tool steels for AM is a promising topic regarding the acceptance of the laser powder bed fusion (PBF-LB) technology for functionally optimized die, forming and cutting tools. In a previous work, the newly developed maraging tool steel FeNiCoMoVTiAl was qualified to be processed by laser powder bed fusion (PBF-LB) with a material density of more than 99.9% using a suitable parameter set. To exploit further optimization potential, the influence of dual-laser processing strategies on the material structure and the resulting mechanical properties was investigated. After an initial calibration procedure, the build data were modified so that both lasers could be aligned to the same scanning track with a defined offset. A variation of the laser-based post-heating parameters enabled specific in-situ modifications of the thermal gradients compared to standard single-laser scanning strategies, leading to corresponding property changes in the produced material structure. An increase in microhardness of up to 15% was thus obtained from 411 HV up to 471 HV. The results of the investigation can be used to derive cross-material optimization potential to produce functionally graded high-performance components on PBF-LB systems with synchronized multi-laser technology. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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16 pages, 16033 KiB  
Article
Sequential Processing of Cold Gas Sprayed Alloys by Milling and Deep Rolling
by Daniel Meyer, Lars Schönemann, Nicole Mensching, Volker Uhlenwinkel and Bernhard Karpuschewski
Materials 2021, 14(13), 3699; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14133699 - 01 Jul 2021
Viewed by 1378
Abstract
Cold gas spraying (CS) is a solid-state material deposition process which, in addition to the flexible repair of individual component areas, also enables the build-up of larger samples. The layers are created on a substrate by the impact-induced bonding of highly accelerated micrometer [...] Read more.
Cold gas spraying (CS) is a solid-state material deposition process which, in addition to the flexible repair of individual component areas, also enables the build-up of larger samples. The layers are created on a substrate by the impact-induced bonding of highly accelerated micrometer particles. Since melting does not occur, the material composition can be varied flexibly and independently of material-specific melting points. In this work, the influence of the described forming process on subsequent machining by milling and deep rolling is investigated. The process forces measured during milling and the surface topography after milling and deep rolling were influenced by the material composition and the CS-related properties, e.g., high material hardness or particle bonding. In contrast to prior assumptions, deep rolling was shown to have no influence on the determined hardness depth profile for the investigated materials. Future work will focus on additional analyses, such as the determination of half-widths, to obtain further insight on the material behavior. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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12 pages, 4988 KiB  
Article
In-Situ Alloy Formation of a WMoTaNbV Refractory Metal High Entropy Alloy by Laser Powder Bed Fusion (PBF-LB/M)
by Florian Huber, Dominic Bartels and Michael Schmidt
Materials 2021, 14(11), 3095; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14113095 - 04 Jun 2021
Cited by 18 | Viewed by 3626
Abstract
High entropy or multi principal element alloys are a promising and relatively young concept for designing alloys. The idea of creating alloys without a single main alloying element opens up a wide space for possible new alloy compositions. High entropy alloys based on [...] Read more.
High entropy or multi principal element alloys are a promising and relatively young concept for designing alloys. The idea of creating alloys without a single main alloying element opens up a wide space for possible new alloy compositions. High entropy alloys based on refractory metals such as W, Mo, Ta or Nb are of interest for future high temperature applications e.g., in the aerospace or chemical industry. However, producing refractory metal high entropy alloys by conventional metallurgical methods remains challenging. For this reason, the feasibility of laser-based additive manufacturing of the refractory metal high entropy alloy W20Mo20Ta20Nb20V20 by laser powder bed fusion (PBF-LB/M) is investigated in the present work. In-situ alloy formation from mixtures of easily available elemental powders is employed to avoid an expensive atomization of pre-alloyed powder. It is shown that PBF-LB/M of W20Mo20Ta20Nb20V20 is in general possible and that a complete fusion of the powder mixture without a significant number of undissolved particles is achievable by in-situ alloy formation during PBF-LB/M when selecting favorable process parameter combinations. The relative density of the samples with a dimension of 6 × 6 × 6 mm3 reaches, in dependence of the PBF-LB/M parameter set, 99.8%. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) measurements confirm the presence of a single bcc-phase. Scanning electron microscopy (SEM) images show a dendritic and/or cellular microstructure that can, to some extent, be controlled by the PBF-LB/M parameters. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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16 pages, 5458 KiB  
Article
Adjustment of Mechanical Properties of Medium Manganese Steel Produced by Laser Powder Bed Fusion with a Subsequent Heat Treatment
by Lena Heemann, Farhad Mostaghimi, Bernd Schob, Frank Schubert, Lothar Kroll, Volker Uhlenwinkel, Matthias Steinbacher, Anastasiya Toenjes and Axel von Hehl
Materials 2021, 14(11), 3081; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14113081 - 04 Jun 2021
Cited by 6 | Viewed by 2531
Abstract
Medium manganese steels can exhibit both high strength and ductility due to transformation-induced plasticity (TRIP), caused by metastable retained austenite, which in turn can be adjusted by intercritical annealing. This study addresses the laser additive processability and mechanical properties of the third-generation advanced [...] Read more.
Medium manganese steels can exhibit both high strength and ductility due to transformation-induced plasticity (TRIP), caused by metastable retained austenite, which in turn can be adjusted by intercritical annealing. This study addresses the laser additive processability and mechanical properties of the third-generation advanced high strength steels (AHSS) on the basis of medium manganese steel using Laser Powder Bed Fusion (LPBF). For the investigations, an alloy with a manganese concentration of 5 wt.% was gas atomized and processed by LPBF. Intercritical annealing was subsequently performed at different temperatures (630 and 770 °C) and three annealing times (3, 10 and 60 min) to adjust the stability of the retained austenite. Higher annealing temperatures lead to lower yield strength but an increase in tensile strength due to a stronger work-hardening. The maximum elongation at fracture was approximately in the middle of the examined temperature field. The microstructure and properties of the alloy were further investigated by scanning electron microscopy (SEM), hardness measurements, X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and element mapping. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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11 pages, 3156 KiB  
Article
Turning of Additively Manufactured Ti6Al4V: Effect of the Highly Oriented Microstructure on the Surface Integrity
by Lucia Lizzul, Rachele Bertolini, Andrea Ghiotti and Stefania Bruschi
Materials 2021, 14(11), 2842; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14112842 - 26 May 2021
Cited by 6 | Viewed by 1810
Abstract
Additive manufacturing processes induce a high orientation in the microstructure of the printed part due to the strong thermal gradients developed during the process caused by the highly concentrated heat source that is used to melt the metal powder layer-by-layer. The resulting microstructural [...] Read more.
Additive manufacturing processes induce a high orientation in the microstructure of the printed part due to the strong thermal gradients developed during the process caused by the highly concentrated heat source that is used to melt the metal powder layer-by-layer. The resulting microstructural anisotropy may have an effect on the post-processing operations such as machining ones. This paper investigates the influence of the anisotropy in turning operations carried out on laser powder bed fused Ti6Al4V parts manufactured with different scanning strategies. The machinability under both transverse and cylindrical turning operations was assessed in terms of surface integrity, considering both surface and sub-surface aspects. The effect of the different cooling conditions, that is flood and cryogenic ones, was studied as well. The outcomes showed that the microstructural anisotropy had a remarkable effect on the machining operations and that the cryogenic cooling enhanced the effect of the anisotropy in determining the surface integrity. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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